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Phenotypic plasticity and exotic plant invasions: Effects of soil nutrients, species nutrient requirements, and types of traits

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Abstract

High phenotypic plasticity has long been considered as a characteristic promoting exotic plant invasions. However, the results of the studies testing this hypothesis are still inconsistent. Overlooking the effects of species resource requirements and environmental resource availability may be the main reasons for the ambiguous conclusions. Here, we compared phenotypic plasticity between five noxious invasive species with different nutrient requirements (evaluated using the soil nutrient status of their natural distribution ranges) and their phylogenetically‐related natives under five nutrient levels. We found that species with high nutrient requirements showed greater plasticity of total biomass than species with low nutrient requirements, regardless of their status (invasive or native). Invasives with high nutrient requirements had greater growth plasticity than their related natives, which may contribute to their invasiveness under high‐nutrient environments. However, compared to the related natives, a higher growth plasticity may not help exotic species with low nutrient requirements to invade nutrient‐rich habitats, and exotic species with high nutrient requirements to invade nutrient‐limited habitats. In contrast, invasives with low nutrient requirements exhibited lower growth plasticity than their related natives, contributing to their invasiveness under nutrient‐limited habitats. Functional traits showed growth‐related plasticity in only 10 cases (3.8%), and there was no functional trait whose plastic response to soil nutrients was beneficial to exotic plant invasions. Our study indicates that low growth plasticity could also promote exotic plant invasions, high plasticity may not necessarily lead to invasiveness. We must test the adaptive significance of plasticity of functional traits when studying its biological roles.

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... Phenotype and resource allocation strategies of invasive plants can influence their adaption to changing environments, which in turn affects their invasion and expansion in various ecosystems. Phenotypic plasticity is one key attribute allowing alien plants to inhabit different and changing environments (Hulme Philip, 2008;Sultan, 2004;Wang et al., 2022). Transgenerational plasticity (TGP) describes the process by which parent organisms influence the phenotypic expression of their offspring through nongenetic means. ...
... TGP is a potential mechanism underlying the rapid spread of many exotic plants to diverse habitats (Helenurm & Schaal, 1996;Rasmann et al., 2012). Intergenerational plasticity often determines the rate and magnitude of the spread of invasive plants (Zhou et al., 2012), particularly for cosmopolitan invasive plants with wide ecological amplitude (Galloway, 2005;Sultan et al., 2009;Wang et al., 2022). Most previous studies on TGP in invasive plants have been conducted mainly on clonal species (Chen et al., 2019;Dong et al., 2017). ...
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Transgenerational plasticity (TGP) allows a plant to acclimate to external variable environments and is a potential mechanism that explains the range expansion and invasion success of some exotic plants. Most studies explored the traits of TGP associated with the success of exotic plant invasions by comparison studies among exotic, native, invasive, and noninvasive species. However, studies on the TGP of invasive plants in different resource environments are scarce, and the biological mechanisms involved are not well understood. This study aimed to determine the role of TGP in the invasiveness of Xanthium strumarium in northeast China. We measured the plant morphology of aboveground parts and the growth of three generations of the invader under different environmental conditions. The results showed that the intergenerational plasticity of X. strumarium was stronger under stress conditions. We found that the X. strumarium parent generation (F0) grown under water and/or nutrient deficiency conditions transferred the environmental information to their offspring (F1 and F2). The F1 generation grown under high‐resource conditions has greater height with larger crown sizes, thicker basal diameters, and higher biomass. Both water and nutrients can affect the intergenerational transmission of plant plasticity, nutrients play a more important role compared with water. The high morphological intergenerational plasticity of X. strumarium under a pressure environment can help it quickly adapt to the new environment and accelerate the rapid expansion of the population in the short term. The root:shoot ratio and reproductive and nutrient distribution of the X. strumarium F0 and F1 generations showed high stability when the growth environment of the F0 generation differed from that of the F1 generation. The stable resource allocation strategy can ensure that the obtained resources are evenly distributed to each organ to maintain the long‐term existence of the community. Therefore, the study of intergenerational transmission plasticity is of great significance for understanding the invasion process, mechanism, and prevention of invasive plants.
... However, additional studies are needed to distinguish the effects of climate and soil on the morphological diversity of these species. This study did not investigate anthropogenic variables and other factors that might have a role in the morphological differentiation of the species and was advocated by Ref. [79]. For example, human disturbances (like fire and pruning), chronic grazing by herbivores (livestock animals), and insect defoliation may contribute to species trait diversity, especially given that the studied populations do not exist inside protected areas. ...
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Plant functional traits are consistently linked with certain ecological factors (i.e., abiotic and biotic), determining which components of a plant species pool are assembled into local communities. In this sense, non-native naturalized plants show more plasticity of morphological traits by adopting new habitat (an ecological niche) of the invaded habitats. This study focuses on the biomass allocation pattern and consistent traits-environment linkages of a naturalized Datura innoxia plant population along the elevation gradient in NW, Pakistan. We sampled 120 plots of the downy thorn apple distributed in 12 vegetation stands with 18 morphological and functional biomass traits during the flowering season and were analyzed along the three elevation zones having altitude ranges from 634.85 m to 1405.3 m from sear level designated as Group I to III identified by Ward's agglomerative clustering strategy (WACS). Our results show that many morphological traits and biomass allocation in different parts varied significantly (p < 0.05) in the pair-wise comparisons along the elevation. Likewise, all plant traits decreased from lower (drought stress) to high elevation zones (moist zones), suggesting progressive adaptation of Datura innoxia with the natural vegetation in NW Pakistan. Similarly, the soil variable also corresponds with the trait's variation e.g., significant variations (P < 0.05) of soil organic matter, organic carbon, Nitrogen and Phosphorus was recorded. The trait-environment linkages were exposed by redundancy analysis (RDA) that was co-drive by topographic (elevation, r = −0.4897), edaphic (sand, r = -0.4565 and silt, r = 0.5855) and climatic factors. Nevertheless, the influences of climatic factors were stronger than soil variables that were strongly linked with elevation gradient. The study concludes that D. innoxia has adopted the prevailing environmental and climatic conditions, and further investigation is required to evaluate the effects of these factors on their phytochemical and medicinal value.
... It generally invades disturbed habitats with nitrate as dominant soil N form. It has been reported that atmospheric nitrate deposition increases by about two times in China since 1985 (Yu et al. 2019), which may increase invasion risk of the invader (Wang et al. 2022b). In this study, we tested the hypothesis that the invader has stronger plastic responses to nitrate addition at high level than its native congener, and further investigated the molecular bases for its stronger plasticity. ...
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Main conclusion High expressions of nitrate use and photosynthesis-related transcripts contribute to the stronger plasticity to high nitrate for the invader relative to its native congener, which may be driven by hormones. Abstract Strong phenotypic plasticity is often considered as one of the main mechanisms underlying exotic plant invasions. However, few studies have been conducted to investigate the related molecular mechanisms. Here, we determined the differences in the plastic responses to high nitrate between the invasive plant X. strumarium and its native congener, and the molecular bases by transcriptome analysis and quantitative real-time PCR validation. Our results showed that the invader had higher plasticity of growth, nitrogen accumulation and photosynthesis in responses to high nitrate than its native congener. Compared with its congener, more N utilization-related transcripts, including nitrate transporter 1/peptide transporter family 6.2 and nitrate reductase 1, were induced by high nitrate in the root of X. strumarium, improving its N utilization ability. More transcripts coding for photosynthetic antenna proteins were also induced by high nitrate in the shoot of X. strumarium, enhancing its photosynthesis. Hormones may be involved in the regulation of the plastic responses to high nitrate in the two species. Our study contributes to understanding the molecular mechanisms underlying the stronger plasticity of the invader in responses to high nitrate, and the potential function of plant hormones in these processes, providing bases for precise control of invasive plants using modern molecular techniques.
... The study also revealed that C. procera exhibited plastic responses in the functional traits and foliar nutrient contents in different urban habitats, which reflected the variations in soil resource gradients. Wang et al. (2022) noticed that invasive and native species demonstrated a similar trend in the effect of nutrient requirements on total biomass plasticity. Species with high nutrient demands demonstrate more total biomass plasticity in comparison to those with low nutrient needs. ...
... (2) increasing the soil microbial activity when compared with the noninvaded habitat through functional redundancy process or in other words the "AMF-host pairing specificity" [10]; (3) increasing nutrient content, thus benefiting plant nutrition, and some microorganisms T A B L E 2 Spores of AMF (spores g soil −1 ) and biodiversity indices observed in the invaded and non-invaded environments by Cryptostegia madagascariensis at tropical Cambisols, Pombal, Paraiba, Northeastern Brazil. adapted to fertile soils [34]; (4) by creating positive AMFsoil-plant feedback which promotes an adapted cycle for the invader's benefit [35]. ...
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Invasive alien plant species (IAPS) have the ability to change the biochemical properties and the arbuscular mycorrhizal fungal (AMF) community structure in their rhizosphere. Organic acids, microbial activity, and AMF play a key role in the invader's spread and also has interactions with the soil chemical factors. Our aim here was to assess the rhizosphere's biochemical factors, AMF community composition, and soil chemical properties associated with Cryptostegia madagascariensis (IAPS) and Mimosa tenuiflora (endemic plant species) from the Brazilian Seasonal Dry Forest. The highest values of total glomalin (5.87 mg g-1 soil), root colonization (54.5%), oxalic and malic acids (84.21 and 3.01 μmol g-1 , respectively), microbial biomass C (mg kg-1 ), Na+ (0.080 cmolc kg-1 ), Ca2+ (7.04 cmolc kg-1 ), and soil organic carbon (4.59 g kg-1 ) were found in the rhizosphere of C. madagascariensis. We found dissimilarities on AMF community structure considering the studied plant species: (i) Racocetra coralloidea, Dentiscutata heterogama, Dentiscutata cerradensis, Gigaspora decipiens, and AMF's richness were highly correlated with the rhizosphere of M. tenuiflora; and (ii). The rhizosphere of C. madagascariensis was highly correlated with the abundance of Claroideoglomus etunicatum, Rhizoglomus aggregatum, Funneliformis mosseae, and Funneliformis geosporum. The results of our study highlight the importance of considering C. madagascariensis as potential hosts for AMF species from Glomerales, and a potential plant species that increase the bioavailability of exchangeable Na and Ca at semi-arid conditions.
... Like many other invasion hypotheses, the phenotypic plasticity hypothesis has mixed support (Davidson et al. 2011, Palacio-López andGianoli 2011); however, Torchyk and Jeschke (2018) suggested a relatively high level of support for this hypothesis compared to others. Discrepancies may be due to the absence of consideration of relevant functional traits (Castillo et al. 2021, Wang et al. 2022. Fewer studies have compared invasive and non-invasive populations, and most of these investigations have focused on plants. ...
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With the advent of the Anthropocene, biological invasions have reached an unprecedented level, and the number of species introductions is still increasing in an ever-changing world. Despite major advances in invasion science, significant debate and lack of clarity remain surrounding the determinants of success of introduced species, the magnitude and dimensions of their impact, and the mechanisms sustaining successful invasions. Empirical studies show divergent impacts of alien populations on ecosystems and contrasting effects of biotic and abiotic factors on the dynamics of alien populations, which hinders the creation of a unified theory of biological invasions. Compounding these issues is the plethora of hypotheses that aim to explain invasion success, which can be unclear and contradictory. We propose a synthesis that categorizes hypotheses along a timeline of invasion. We sorted invasion hypotheses along the invasion timeline, and considered population, community and ecosystem levels. This temporal sorting of invasion concepts shows that each is relevant at a specific stage of the invasion. Although concepts and empirical findings on alien species may appear contradictory, when mapped onto an invasion timeline, they may be combined in a complementary way. An overall scheme is proposed to summarise the theoretical dynamics of ecosystems subjected to invasions. For any given case study, this framework provides a guide through the maze of theories and should help choose the appropriate concepts according to the stage of invasion.
... Like many other invasion hypotheses, the phenotypic plasticity hypothesis has mixed support (Davidson et al. 2011, Palacio-López andGianoli 2011); however, Torchyk and Jeschke (2018) suggested a relatively high level of support for this hypothesis compared to others. Discrepancies may be due to the absence of consideration of relevant functional traits (Castillo et al. 2021, Wang et al. 2022. Fewer studies have compared invasive and non-invasive populations, and most of these investigations have focused on plants. ...
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Biological invasions have reached an unprecedented level and the number of introduced species is still increasing worldwide. Despite major advances in invasion science, the determinants of success of introduced species, the magnitude and dimensions of their impact, and the mechanisms sustaining successful invasions are still debated. Empirical studies show divergent impacts of non-native populations on ecosystems and contrasting effects of biotic and abiotic factors on the dynamics of non-native populations; this is hindering the emergence of a unified theory of biological invasions. We propose a synthesis that merges perspectives from population, community, and ecosystem levels. Along a timeline of ecosystem transformation driven by non-native species, from historical to human-modified ecosystems, we order invasion concepts and theories to clarify their chaining and relevance during each step of the invasion process. This temporal sorting of invasion concepts shows that each concept is relevant at a specific stage of the invasion. Concepts and empirical findings on non-native species may appear contradictory. However, we suggest that, when mapped onto an invasion timeline, they may be combined in a complementary way. An overall scheme is proposed to summarise the theoretical dynamics of ecosystems subjected to invasions. For any given case study, this framework provides a guide through the maze of theories and should help choose the appropriate concepts according to the stage of invasion.
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The effect of UV-B radiation exposure on transgenerational plasticity, the phenomenon whereby the parental environment influences both the parent’s and the offspring’s phenotype, is poorly understood. To investigate the impact of exposing successive generations of rice plants to UV-B radiation on seed morphology and proanthocyanidin content, the local traditional rice variety ‘Baijiaolaojing’ was planted on terraces in Yuanyang county and subjected to enhanced UV-B radiation treatments. The radiation intensity that caused the maximum phenotypic plasticity (7.5 kJ·m−2) was selected for further study, and the rice crops were cultivated for four successive generations. The results show that in the same generation, enhanced UV-B radiation resulted in significant decreases in grain length, grain width, spike weight, and thousand-grain weight, as well as significant increases in empty grain percentage and proanthocyanidin content, compared with crops grown under natural light conditions. Proanthocyanidin content increased as the number of generations of rice exposed to radiation increased, but in generation G3, it decreased, along with the empty grain ratio. At the same time, biomass, tiller number, and thousand-grain weight increased, and rice growth returned to control levels. When the offspring’s radiation memory and growth environment did not match, rice growth was negatively affected, and seed proanthocyanidin content was increased to maintain seed activity. The correlation analysis results show that phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), dihydroflavonol 4-reductase (DFR), and 4-coumarate:CoA ligase (4CL) enzyme activity positively influenced proanthocyanidin content. Overall, UV-B radiation affected transgenerational plasticity in seed morphology and proanthocyanidin content, showing that rice was able to adapt to this stressor if previous generations had been continuously exposed to treatment.
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Functional traits, their plasticity and their integration in a phenotype have profound impacts on plant performance. We developed structural equation models (SEMs) to evaluate their relative contribution to promote invasiveness in plants along resource gradients. We compared 20 invasive-native phylogenetically and ecologically related pairs. SEMs included one morphological (root-to-shoot ratio (R/S)) and one physiological (photosynthesis nitrogen-use efficiency (PNUE)) trait, their plasticities in response to nutrient and light variation, and phenotypic integration among 31 traits. Additionally, these components were related to two fitness estimators, biomass and survival. The relative contributions of traits, plasticity and integration were similar in invasive and native species. Trait means were more important than plasticity and integration for fitness. Invasive species showed higher fitness than natives because: they had lower R/S and higher PNUE values across gradients; their higher PNUE plasticity positively influenced biomass and thus survival; and they offset more the cases where plasticity and integration had a negative direct effect on fitness. Our results suggest that invasiveness is promoted by higher values in the fitness hierarchy--trait means are more important than trait plasticity, and plasticity is similar to integration--rather than by a specific combination of the three components of the functional strategy.
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The effect of soil nutrients on the invasion of alien plants is a hot topic in invasion biology research, but few studies have focused on the effects of soil nutrients on the characteristics of reciprocally crossing plants. In this study, we analyzed the differences in biomass accumulation and distribution, growth characteristics, and photosynthetic characteristics of the invasive plant Xanthium strumarium, the native plant Xanthium sibiricum, and their reciprocal crosses (Xst♀×Xsi♂ and Xsi♀×Xst♂) under different nitrogen treatments, to explore the relationship between invasion and soil nutrient status. The stem diameter, total leaf area, total biomass, root biomass, root biomass ratio, and root mass/crown mass ratio of X. strumarium, X. sibiricum, and their reciprocal crosses (Xst♀×Xsi♂) increased significantly (P<0.05) and the leaf area to root mass ratio decreased significantly (P<0.05) with increasing nitrogen levels in the soil. The net assimilation rate of X. strumarium was significantly higher than that of X. sibiricum (P<0.05), but its specific leaf area was significantly lower than that of X. sibiricum (P<0.05). The relative growth rate, net assimilation rate, and mean leaf area ratio were higher in the male progeny than in the female progeny (P<0.05), and the biomass index and growth index were higher in Xst♀×Xsi♂ plants than in Xsi♀ × Xst♂ plants. We concluded that: 1) when nutrients are limited, X. strumarium distributes more biomass to the root, possibly as an ecological strategy to adapt to nutrient-heterogenous environments during invasion. 2) Compared with the hybrid progenies of X. sibiricum, those of X. strumarium show stronger growth and increased reproductive ability, which are properties that will further strengthen their invasiveness.
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We explored the roles of phenotypic plasticity and competition in contributing to the success of Eupatorium catarium, a recently invasive noxious annual forb in South China. We compared the growth and functional traits of E. catarium with those of a common native plant, Vernonia cinerea, and a long-term historic invader, Ageratum conyzoides, along a nutrient gradient under both competitive and non-competitive conditions. Under non-competitive conditions, biomass differed little between species under low-nutrient conditions. However, nutrient addition resulted in a greater increase in biomass of the two invasive species than that of V. cinerea. The greater increase in biomass in the two invasive plants may be partly explained by their greater plasticity in specific leaf area. The competition experiments involved different combinations of species: plants of E. catarium were grown with either a plant of A. conyzoides or with a plant of V. cinerea, or individual plants of all three species were grown in competition with a grassland sward grown from 1.5 g seeds of Digitaria radicosa. Relative to non-competitive conditions, competition further increased the biomass difference between the two invasive plants and V. cinerea under high nutrient conditions. A. conyzoides outcompeted E. catarium in terms of biomass production under high nutrient conditions. Overall, these results indicate that A. conyzoides and E. catarium tend to outperform V. cinerea under high nutrient conditions and in both competitive and non-competitive environments. However, E. catarium cannot outperform A. conyzoides in terms of biomass production under each of the nutrient and competitive conditions.
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Xanthium sibiricum, an annual weed, unexpectedly and dramatically occupied the exposed drawdown area after water had been impounded for the first time in the newly created Three Gorges Reservoir in China. In order to explain this phenomenon and establish an appropriate management strategy, the effects of constant submersion on seed viability and germination of X. sibiricum were investigated at two constant temperature regimes (25°C and 30°C) under artificial laboratory conditions. The results indicated that the seeds of X. sibiricum exhibited a high level of tolerance of submersion and up to 99% of seeds were viable in each treatment regime. The effect of submersion on germination was not obvious at 25°C until the submersion was prolonged for 180 days, while at 30°C the eventual germination rate of X. sibiricum, even after submergence for only one day, was significantly improved. The speed of germination was also consistently accelerated by prolonged periods of submersion. The proportion of seeds that germinated in all treatments combined was less that 56% due to seed dimorphism, thereby providing a seed bank. We conclude that the interaction between long-term winter flooding and high temperature in summer is the major reason that X. sibiricum was able to occupy the newly exposed drawdown area in the absence of competition. These findings provided further insight into how germination strategy and reservoir water-management regime contributed to this dramatic species outbreak.
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QuestionsThe link between the carbon composition of aquatic plants and (1) plant strategies and (2) habitat nutrient availability has received little attention. We tested whether three aquatic species belonging to the three adaptive strategies defined by Grime (ruderal, stress tolerant and competitive) had contrasting carbon allocation patterns, and if these patterns varied in the same way between populations distributed along a gradient of habitat nutrient content.LocationWetlands in the northern Rhône River Basin, France.Methods The three species were sampled in 17 wetlands along a gradient of nutrient content in the northern Rhône River Basin. In each population sampled, we measured plant water content, C/N ratio, structural compounds (lignin and structural polysaccharides) and storage compounds (free sugars and starch) in two seasons (spring and autumn 2012).ResultsThe stress-tolerant species had higher content of structural compounds than the competitive and ruderal species. The content of storage compounds was higher in the competitive and stress-tolerant species compared to the ruderal species. Allocation of carbon compounds varied with habitat nutrient content in different ways for the three species, suggesting contrasting plasticities, possibly linked to plant strategy.Conclusion Plant strategies and habitat nutrient content are likely key drivers in plant carbon allocation and should be taken into account when studying interactions between habitat and plant quality.
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The reaction of seven grass species to variations in nitrate nitrogen concentration was studied in sand culture. The species showed very marked differences in yield response. Lolium perenne and Agrostis stolonifera showed the greatest response and yielded most at the highest level used (243 ppm N). Agrostis tenuis showed a response similar to that of Lolium perenne at low nitrogen levels but was significantly less responsive at high levels; there was, however, a significant difference between the response of lead resistant and normal populations of Agrostis tenuis. The response of Cynosurus cristatus and Festuca ovina was significantly less than the above species at low nitrogen levels and both species were adversely affected by the highest level (243 ppm N). Agrostis canina was very responsive to nitrogen at the lower levels but failed to respond to nitrogen above 27 ppm N. Nardus stricta responded only weakly up to 27 ppm N and showed a very strong depression of yield above this level. The response of the various species to nitrogen in sand culture shows a considerable measure of agreement with determinations of nitrogen response made by other investigators in fertilizer trials and in studies of the correlation between species distribution and soil nitrogen levels in permanent pastures. It is concluded that variation in soil nitrogen levels is probably an important factor determining the distribution of plant species under natural conditions. The possible ecological significance of differences in overall yield between species is discussed in relation to levels of soil fertility.
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Interannual variability in climatic conditions should be taken into account in climate change studies in semi‐arid ecosystems. It may determine differentiation in phenotypic plasticity among populations, with populations experiencing higher environmental heterogeneity showing higher levels of plasticity. The ability of populations to evolve key functional traits and plasticity may determine the survival of plant populations under the drier and more variable climate expected for semi‐arid ecosystems. Working with populations of the semi‐arid Chilean shrub Senna candolleana along its entire distribution range, we assessed inter‐ and intra‐population variation in functional traits as well as in their plasticity in response to water availability. We measured morphological and physiological traits related to drought resistance in both field conditions and in a greenhouse experiment, where drought response was evaluated under two water availability treatments. All populations responded plastically, but higher precipitation heterogeneity in dry‐edge populations seemed to have selected for more plastic genotypes compared to populations growing at mesic sites and with more homogeneous environmental conditions. Synthesis. Our results suggest adaptive plasticity since higher levels of phenotypic plasticity were positively associated with plant performance. However, we did not find evidence for genetic variation for plasticity within populations. To the extent that phenotypic plasticity may play a key role in future persistence, populations at mesic sites may be more vulnerable to climate change due to their lower plasticity and their current limitations to evolve novel norms of reaction. Conversely, although Senna candolleana populations at the dry edge are exposed to higher levels of stress, they may be less susceptible to climate change in view of their greater plasticity. We highlight the need to consider population differentiation in both mean traits and their plasticity to model realistic scenarios of species distribution under climate change.
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The invasiveness of alien plants is closely related to their reproductive characteristics. A comparison of reproductive characteristics of an alien species in different habitats will help to reveal its optimum habitat for invasion and the mechanism of invasion. Furthermore, it will provide a theoretical foundation for planning a reasonable management strategy. Solanum rostratum is a summer annual weed native to the neotropics and the southwestern USA that produces offspring only by sexual reproduction. This species has become established in seven provinces/cities of China, including Xinjiang. We compared reproductive characteristics of S. rostratum in oasis, desert grassland and gravel desert habitats in Xinjiang and determined the optimum habitat for its invasion. The results were as follows. (1) Single-flower duration of S. rostratum was between 27 and 47 hours. Daily flowering time and single-flower duration were similar among the three habitats. However, number of flowers per individual differed among habitats (P<0.01=: oasis > desert grassland > gravel desert. (2) Halictus quadricinctus, Halictus sp. and Xylocopa latipes were the pollinators of S. rostratum, and all of them buzz-pollinated flowers. However, X. latipes visited flowers only occasionally. (3) Total visiting frequency of pollinators differed among habitats (P desert grassland > gravel desert. Halictus quadricinctus preferred habitats with relatively low temperatures and high humidity, while another species of Halictus preferred relatively high temperatures and low humidity. Thus, the daily time of the peak of visiting frequency of H. quadricinctus was earlier than that of Halictus sp. (4) Order of number of fruits per individual, seed number per fruit and per individual and mass of 1,000 seeds was oasis > desert grassland > gravel desert. Fruit number per individual was highly significantly positively correlated with both number of flowers per individual and total visiting frequency of pollinators. Seed numbers per individual and per fruit were significantly positively correlated with total visiting frequency of pollinators. Our study indicates that S. rostratum can obtain more resources, produce more flowers that attract pollinators and produce more seeds with larger mass in oases than in desert grassland or gravel desert. Therefore, the oasis is the optimum habitat of S. rostratum in the arid region of Xinjiang, China.
Article
Plant communities can respond to environmental changes by altering their species composition and by individuals (within species) adjusting their physiology. These responses can be captured by measuring key functional traits among and within species along important environmental gradients. Some anthropogenic changes (such as fertilizer runoff) are known to induce distinct community responses, but rarely have responses across natural and anthropogenic gradients been compared in the same system. In this study, we used comprehensive specific leaf area (SLA) data from a diverse Australian annual plant system to examine how individual species and whole communities respond to natural and anthropogenic gradients, and to climatically different growing seasons. We also investigated the influence of different leaf-sampling strategies on community-level results. Many species had similar mean SLA values but differed in SLA responses to spatial and temporal environmental variation. At the community scale, we identified distinct SLA responses to natural and anthropogenic gradients. Along anthropogenic gradients, increased mean SLA, coupled with SLA convergence, revealed evidence of competitive exclusion. This was further supported by the dominance of species turnover (vs. intraspecific variation) along these gradients. We also revealed strong temporal changes in SLA distributions in response to increasing growing-season precipitation. These climate-driven changes highlight differences among co-occurring species in their adaptive capacity to exploit abundant water resources during favorable seasons, differences that are likely to be important for species coexistence in this system. In relation to leaf-sampling strategies, we found that using leaves from a climatically different growing season can lead to misleading conclusions at the community scale.
Article
The high potential fitness benefit of phenotypic plasticity tempts us to expect phenotypic plasticity as a frequent adaptation to environmental heterogeneity. Examples of proven adaptive plasticity in plants, however, are scarce and most plastic responses actually may be 'passive' rather than adaptive. This suggests that frequently requirements for the evolution of adaptive plasticity are not met or that such evolution is impeded by constraints. Here we outline requirements and potential constraints for the evolution of adaptive phenotypic plasticity, identify open questions, and propose new research approaches. Important open questions concern the genetic background of plasticity, genetic variation in plasticity, selection for plasticity in natural habitats, and the nature and occurrence of costs and limits of plasticity. Especially promising tools to address these questions are selection gradient analysis, meta-analysis of studies on genotype-by-environment interactions, QTL analysis, cDNA-microarray scanning and quantitative PCR to quantify gene expression, and two-dimensional gel electrophoresis to quantify protein expression. Studying plasticity along the pathway from gene expression to the phenotype and its relationship with fitness will help us to better understand why adaptive plasticity is not more universal, and to more realistically predict the evolution of plastic responses to environmental change.
Article
It is suggested that evolution in plants may be associated with the emergence of three primary strategies, each of which may be identified by reference to a number of characteristics including morphological features, resource allocation, phenology, and response to stress. The competitive strategy prevails in productive, relatively undisturbed vegetation, the stress-tolerant strategy is associated with continuously unproductive conditions, and the ruderal strategy is characteristic of severely disturbed but potentially productive habitats. A triangular model based upon the three strategies may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.
Article
a b s t r a c t The exotic species Bidens frondosa is rapidly spreading in northern Italian arable fields, while Bidens tripartita, a native congeneric, shows less invasive capacity. To characterise and model the phenology of the two species, a two-year study was conducted involving sowings at 15-day intervals between March and August. The length of the sowing-emergence phase was well described by a simple thermal model, with a base temperature of 4.5 • C, for both species. A multiplicative photothermal model was found to be the best for the emergence-flowering phase. B. frondosa resulted as being less macrothermal and more sensitive to photoperiod. The flowering-maturity phase lasted for 30–32 days, on average, and was well described by a model based on soil water availability: this phase shortens when there is a lack of water, particularly in B. tripartita. The more relevant differences between the two species seem to be related to the vegetative phase length, which varied from 150 to 46 days and from 123 to 42 days in B. frondosa and B. tripartita, respectively. Thanks to the high elasticity of its vegetative phase, B. frondosa can grow taller than B. tripartita and acquire higher competitivity and seed production potential, both relevant factors in determining the success of a species.
Article
1. Plastic responses to spatiotemporal environmental variation strongly influence species distribution, with widespread species expected to have high phenotypic plasticity. Theoretically, high phenotypic plasticity has been linked to plant invasiveness because it facilitates colonization and rapid spreading over large and environmentally heterogeneous new areas. 2. To determine the importance of phenotypic plasticity for plant invasiveness, we compare well-known exotic invasive species with widespread native congeners. First, we characterized the phenotype of 20 invasive–native ecologically and phylogenetically related pairs from the Mediterranean region by measuring 20 different traits involved in resource acquisition, plant competition ability and stress tolerance. Second, we estimated their plasticity across nutrient and light gradients. 3. On average, invasive species had greater capacity for carbon gain and enhanced performance over a range of limiting to saturating resource availabilities than natives. However, both groups responded to environmental variations with high albeit similar levels of trait plasticity. Therefore, contrary to the theory, the extent of phenotypic plasticity was not significantly higher for invasive plants. 4. We argue that the combination of studying mean values of a trait with its plasticity can render insightful conclusions on functional comparisons of species such as those exploring the performance of species coexisting in heterogeneous and changing environments.
Article
Phenotypic plasticity is commonly considered as a trait associated with invasiveness in alien plants because it may enhance the ability of plants to occupy a wide range of environments. Although the evidence of greater phenotypic plasticity in invasive plants is considerable, it is not yet conclusive. We used a meta-analysis approach to evaluate whether invasive plant species show greater phenotypic plasticity than their native or non-invasive counterparts. The outcome of such interspecific comparisons may be biased when phylogenetic relatedness is not taken into account. Consequently, species pairs belonged to the same genus, tribe or family. The meta-analysis included 93 records from 35 studies reporting plastic responses to light, nutrients, water, CO2, herbivory and support availability. Contrary to what is often assumed, overall, phenotypic plasticity was similar between invasive plants and native or non-invasive closely related species. The same result was found when separate analyses were conducted for trait plasticity to nutrients, light and water availability. Thus, invasive plant species and their native or non-invasive counterparts are equally capable of displaying functional responses to environmental heterogeneity. The colonization of a wide range of environments by invasive plants could be due to their capacity to undergo adaptive ecotypic differentiation rather than to their ability to display plastic responses. Alternatively, phenotypic plasticity might play a role in plant invasion, but only during the initial phases, when tolerance of the novel environment is essential for plant survival. Afterwards, once alien plants are identified as invaders, the magnitude of phenotypic plasticity might be reduced after selection of the optimum phenotypes in each habitat. The identification of plant traits that consistently predict invasiveness might be a futile task because different traits favor invasiveness in different environments. Approaches at the local scale, focusing on the ecology of specific invasive plants, could be more fruitful than global macro-analyses.
Article
Summary • Phenotypic plasticity is often cited as an important mechanism of plant invasion. However, few studies have evaluated the plasticity of a diverse set of traits among invasive and native species, particularly in low resource habitats, and none have examined the functional significance of these traits. • I explored trait plasticity in response to variation in light and nutrient availability in five phylogenetically related pairs of native and invasive species occurring in a nutrient-poor habitat. In addition to the magnitude of trait plasticity, I assessed the correlation between 16 leaf- and plant-level traits and plant performance, as measured by total plant biomass. Because plasticity for morphological and physiological traits is thought to be limited in low resource environments (where native species usually display traits associated with resource conservation), I predicted that native and invasive species would display similar, low levels of trait plasticity. • Across treatments, invasive and native species within pairs differed with respect to many of the traits measured; however, invasive species as a group did not show consistent patterns in the direction of trait values. Relative to native species, invasive species displayed high plasticity in traits pertaining to biomass partitioning and leaf-level nitrogen and light use, but only in response to nutrient availability. Invasive and native species showed similar levels of resource-use efficiency and there was no relationship between species plasticity and resource-use efficiency across species. • Traits associated with carbon fixation were strongly correlated with performance in invasive species while only a single resource conservation trait was strongly correlated with performance in multiple native species. Several highly plastic traits were not strongly correlated with performance which underscores the difficulty in assessing the functional significance of resource conservation traits over short timescales and calls into question the relevance of simple, quantitative assessments of trait plasticity. • Synthesis. My data support the idea that invasive species display high trait plasticity. The degree of plasticity observed here for species occurring in low resource systems corresponds with values observed in high resource systems, which contradicts the general paradigm that trait plasticity is constrained in low resource systems. Several traits were positively correlated with plant performance suggesting that trait plasticity will influence plant fitness.
Article
Little is known about the traits and mechanisms that determine whether or not a species will be invasive. Invasive species are those that establish and spread after being introduced to a novel habitat. A number of previous studies have attempted to correlate specific plant traits with invasiveness. However, many such studies may be flawed because they fail to account for shared evolutionary history or fail to measure performance directly. It is also clear that performance is context dependent. Thus, an approach that corrects for relatedness and incorporates multiple experimental conditions will provide additional information on performance traits of invasive species. I use this approach with two or three pairs of invasive and closely related non‐invasive species of Commelinaceae grown over experimental gradients of nutrient and water availability. Invasive species have been introduced, established, and spread outside their native range; non‐invasive species have been introduced, possibly (but not necessarily) established, but are not known to have spread outside their native range. The invasive species had higher relative growth rates (RGR) than non‐invasive congeners at high nutrient availabilities, but did not differ from non‐invasive species at low nutrient availabilities. This is consistent with a strategy where these particular invasive species are able to rapidly use available resources. Relative growth rates were also higher for two out of three invasive species across a water availability gradient, but RGR did not differ in plasticity between the invasive and non‐invasive species. This suggests that nutrient addition, but not changes in water availability, might favour invasion of dayflowers. This approach is novel in comparing multiple pairs of invasive and non‐invasive congeners across multiple experimental conditions and allows evaluation of the robustness of performance differences. It also controls for some of the effects of relatedness that might confound multispecies comparisons.
Article
We tested the hypotheses that invasive species had higher irradiance plasticity, capture ability and efficiency than noninvasive species using two invasive aliens – Ageratina adenophora and Chromolaena odorata, and one noninvasive alien – Gynura sp. The three aliens were grown at 4.5%, 12.5%, 36%, 50% and 100% irradiances for 64 days before harvesting. The plastic response of specific leaf area (SLA) contributed to improved light interception at low irradiance, carbon gain and water balance at high irradiance. It was a good predictor for intraspecific irradiance responses of leaf area ratio (LAR), leaf area:root mass ratio, maximum photosynthetic rate (Pmax) and net assimilation rate (NAR). Biomass allocation-related traits were species specific and their plasticity to irradiance was low. The high root mass fraction, leaf mass fraction and LAR distinguished the two invaders from Gynura. However, other resource capture-related traits, such as SLA, NAR and Pmax, were not always higher for the invaders than for Gynura. Furthermore, plasticity to irradiance was not different between the invasive and noninvasive aliens. With increasing irradiance, Gynura decreased biomass investment to roots and leaves but increased the investment to support structures adversely affecting both low and high irradiance acclimation. Ageratina might invade new habitat successfully through tolerating shading at low irradiance and outshading competitors by forming dense stands when irradiance is increased. The results suggested that both resource capture-related traits and irradiance acclimation conferred competitive advantage to the two invaders and some traits were common for invasive and noninvasive aliens but others were specific for invaders.
Article
We evaluated in common-garden experiments the morphological plasticity to shading of three Convolvulus species that occur in Chile and differ in ecological breadth. Convolvulus arvensis L. is a world weed distributed along the country, and is found in open as well as in shaded habitats. Convolvulus chilensis Pers. is a Chilean endemic species typical of coastal habitats, and is found in open to partially open sites. C. demissus choisy occurs only on slopes of the Andes of Chile and Argentina, habitats with high incidence of solar radiation. We hypothesized that the magnitude of phenotypic plasticity to shading of these species would correlate with their ecological breadth. Shading had a significant effect on internode length, petiole length, stem diameter, stem length, number of branches, leaf area, leaf shape, leaf biomass, and specific leaf area. Species differed in all the morphological traits except leaf biomass. A significant Shading × Species interaction in the two-way ANOVA, i.e. differential plasticity to shading of Convolvulus species, was found for petiole length, stem length, number of branches, leaf shape, and specific leaf area. Contrary to our hypothesis, tests of parallelism showed that, in general, the plasticity to shading of C. chilensis (the species of intermediate ecological breadth) was the greatest, and that of C. arvensis (the weed) and C. demissus (the species of narrow distribution) was similar. Issues of ecotype differentiation, in the case of C. arvensis, and the role of life history traits are raised to explain the observed lack of association between ecological breadth and magnitude of phenotypic plasticity.
Article
Summary • Phenotypic plasticity has long been suggested to facilitate biological invasions where a general purpose genotype or ‘Jack-of-all-trades’ strategy could facilitate invasion should native species be, on average, more specialized. Current understanding of the importance of phenotypic plasticity is limited by methodological difficulties yet glasshouse experiments, paralleling those used in evolutionary biology, are increasingly being used to assess whether invasive species have high phenotypic plasticity or not. Unfortunately, these studies have several major limitations. • In general, glasshouse experiments have quantified relatively labile means of expressing phenotypes, such as plant biomass, rather than changes in plant development. As some environments favour plant growth and reproduction more than others, simply quantifying allometric or physiological responses relating to differential plant growth may not reveal much about phenotypic plasticity. • Plasticity is often a comparative rather than an absolute measure. A range of comparators have been used, for example, unrelated natives, congeneric natives, other congeneric aliens or conspecifics from the source region. Thus, unlike many life-history traits used in analyses of invasion, phenotypic plasticity is strongly context-dependent and limits comparison across different studies. • Phenotypic plasticity is assumed to lead to a greater breadth of environmental conditions across which a species can maintain positive population growth and increase the likelihood of invasiveness. Yet, most studies examine only a partial subset of the full environmental range experienced by the species. If the reaction norm of a target species and its comparator vary independently across an environmental gradient, this partial approach can present different interpretations of phenotypic plasticity. • Rather than simply quantifying greater phenotypic plasticity in invasive species, research questions should be directed at better understanding its role in the geographic distribution, successful colonization, population persistence and/or high local abundance of invasive species in the introduced range. These issues require integrated measures of plant performance rather than crude differences in individual traits across an environmental gradient. As yet, there is only limited appreciation of the role of phenotypic plasticity in any one of these areas and there is a need to extend studies beyond glasshouse experiments.
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Do invasive plant species have greater phenotypic plasticity than non-invasive species? And, if so, how does this affect their fitness relative to native, non-invasive species? What role might this play in plant invasions? To answer these long-standing questions, we conducted a meta-analysis using data from 75 invasive/non-invasive species pairs. Our analysis shows that invasive species demonstrate significantly higher phenotypic plasticity than non-invasive species. To examine the adaptive benefit of this plasticity, we plotted fitness proxies against measures of plasticity in several growth, morphological and physiological traits to test whether greater plasticity is associated with an improvement in estimated fitness. Invasive species were nearly always more plastic in their response to greater resource availability than non-invasives but this plasticity was only sometimes associated with a fitness benefit. Intriguingly, non-invasive species maintained greater fitness homoeostasis when comparing growth between low and average resource availability. Our finding that invasive species are more plastic in a variety of traits but that non-invasive species respond just as well, if not better, when resources are limiting, has interesting implications for predicting responses to global change.